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ETL Testing Interview Questions• 5. What is a Data Mart?• 6. What is ETL?• 7. BI/DW Testing• 8. What is the need to test a Data Warehouse?• 9. Data Warehouse Testing and Database Testing• 10. Type of testing done in a Data Warehouse project• 11. Who all are involved in testing a data warehouse?• 12. What are the phases undergone by the QA team?• 13. How does the QA team prepare test cases?• 14. Query Format• 15. OLTP• 16. OLAP• 17. Data mining.• 18. Should we use OLTP design for DWH• 19. Lookup tables

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ETL Testing Interview Questions Query format:Attribute checkSelect count(1)From( Select source table attributesFrom source tableWhere list of conditionsExceptSelect corresponding target table attributesFrom target tableWhere list of conditions)alias(alternate name)Expected output: Count=0In the above query, we are first retrieving all the attributes from source table which are mappedto target and then removing from this list all the attributes that are present in target table. So theresult count should be zero, meaning that all the attributes that are present in source table arepresent in target table and the test case can be passed.

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ETL Testing Interview Questions Query format:Duplicate CheckSelect count(1)From( Select attribute_list_1From table_1Where list of conditionsGroup by attribute_list_1Having count(1)>1)aliasExpected output: Count=0In the above query, we are retrieving the attributes which are supposed to be unique and thengrouping them in the same order in which they were retrieved. This will group all the recordswhich have these attributes duplicated and so the count will be greater than 1 for such records.When we take the count of such duplicate records and we get zero output, then this shows thatthere are no duplicate values for unique columns and the test case can be passed.

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ETL Testing Interview Questions Query format:Original Key CheckSelect count(1)From tableWhere list of conditionsAnd (any of NOT NULL values are NULL)Expected output: Count=0In the above query, we are retrieving all the records which have any of the NOT NULLcolumns as NULL and then taking count of it. If the count is zero, this means there are nosuch records and the test case can be passed.

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ETL Testing Interview Questions Query format:Reconciliation CheckSelect count(*)From source tableWhere list of conditionsSelect count(*)From target tableWhere list of conditionsExpected output: Source count = Target countIn the above check, there are two queries, one fetching the count of total numberof records in source table and the other fetching the count of total number ofrecords in target table. If both the counts are same, this means that there areequal number of records in source and target and the test case can be passed.

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ETL Testing Interview Questions Query format:Relationship CheckSelect count(child_id)From( Select parent_attribute_to_be_checked parent_id,Child_attribute_to_be_checked child_idFrom( Select distinct attributes from child tableLeft outer joinSelect distinct attributes from parent tableOn join conditions))Where parent_id IS NULLExpected output: Count=0In the above query, we are retrieving all the records in target table which has no parent in sourcetable and then taking its count. If the count is zero, this means that there are no such records andthe test case can be passed. Checking lookup condition is the most common example for this typeof check.